German Offenlegungsschrift 2,855,916 describes an apparatus for producing a reaction mixture from fluid components to form a solid or foam material. The apparatus broadly consists of
(a) storage vessels for the components,
(b) feed pipes which connect the storage vessels via
(c) metering pumps to a
(d) mixing chamber arranged in a mixing head into which said feed pipes open via
(e) injectors;
(f) an outlet opening arranged in the mixing chamber,
(g) return pipes with associated shut-off members,
(h) the injectors and the shut-off members being in the form of needle-equipped nozzles which
(j) cooperate with replaceable nozzle seats containing the nozzle orifices;
(k) a separate hydraulic positive control being associated with each nozzle, and
(l) all the nozzles being closed for a short time interval during the changeover from mixing condition to fluid circulation condition and from fluid circulation condition to mixing condition.
This apparatus has proved successful in principle. However, it has an extremely complicated structure because the hydraulic control system has to have two control valves which are designed to be switched through a timing element.
An object of the present invention is to provide an apparatus of the kind mentioned above in which the hydraulic control system is simpler and, hence, less expensive and more reliable in operation.